The present invention relates to a method for making aluminium boiler units for coffee making machines, in particular boiler units having a faceted upwardly tapering side surface.
Among the available aluminium coffee makers, one which has encountered a large success is the commercially available so-called "moka" maker, i.e. a coffee maker comprising a boiler unit having the configuration of a frustum of a pyramid provided with a polygonal bottom, the small base of the pyramid being upwardly facing, the coffee maker also comprising a like, but reversed, top portion.
The mentioned coffee maker is conventionally made by casting or die-casting an aluminium material.
Conventionally, this aluminium material comprises an aluminium alloy having a comparatively high silicon content, for providing, in the casting operation, the necessary flow capability to the metal material in order to faithfully reproduce in the coffee maker being made the details of the hollow of the forming mold.
In particular, the silicon material is necessary to provide a satisfactory casting or die-casting operation.
On the other hand, such a silicon content is undesirable since an aluminium alloy with a comparatively high silicon content is subjected to easy oxidation.